1. Field of the Invention
The present invention relates to a light controlling apparatus and method, and more particularly, to a light controlling apparatus and method for a projector for maintaining a constant luminance level on a display screen.
2. Discussion of the Related Art
Generally, as shown in FIG. 1A, a projector includes a light source driver 1 for driving a light source according to an input control signal CS, a light source 2 having a lamp driven by light source driver 1 and for irradiating a strong light for displaying an image. A converging lens 3 is positioned in front of light source 2 for converging the light irradiated from light source 2. A first polarizing plate 4 is positioned in front of converging lens 3 for initially polarizing the irradiated light. An LCD 5 is positioned near the front of first polarizing plate 4 for displaying an image according to an input video signal. A second polarizing plate 6 is positioned near the front of LCD 5 for subsequently polarizing the light irradiated through LCD 5. A projection lens 7 is positioned in front of second polarizing plate 6 for focusing or zooming an image projected through LCD 5 and second polarizing plate 6. A screen 8 displays the image projected through projection lens 7. The operation of such a projector will be discussed below.
According to the input control signal CS, light source driver 1 controls light source 2, which in turn irradiates a strong light. The light irradiated from light source 2 is converged by converging lens 3 which projects the light onto the back of LCD 5 through first polarizing plate 4. Here, according to an externally input video signal, an image is displayed on LCD 5. This displayed image is in turn displayed on screen 8 through second polarizing plate 6 and projection lens 7 from the light projected through first polarizing plate 4.
Projection lens 7 is installed to control the distance from LCD 5. The focusing of an image displayed on external screen 8 is performed by controlling the distance from projection lens 7.
As shown in FIG. 1B, the angle of light of the image displayed on screen 8 is varied as projection lens 7 is zoomed. Therefore, the size of the image displayed on screen 8 varies. In other words, when field of view becomes larger from .theta.1 to .theta.2 with projection lens 7 zoomed, the size of the image on screen 8 becomes larger, for example, from size A to size B in FIG. 1B.
However, in the conventional projector, control signal CS applied to light source driver 1 is controlled only by a main function selection mode. Hence, when a user enlarges an image displayed on the screen by zooming, its luminance level decreases to dim the image. In addition, when an image is displayed in a bright periphery or surrounding, the luminance level of the image displayed is relatively decreased to produce a dim image, in accordance with the brightness of the periphery.